The concept of flexible wiring for branch circuit power distribution apparently was introduced in the United States in 1939, by Rugg et al in U.S. Pat. No. 2,162,864; the first commercial flexible wiring products, though, are believed not to have been introduced until 1971. The term "flexible wiring" refers to the use of a modular type of wiring system in which flexible cable sets are used to interconnect light fixtures, switches, receptacles, etc. The cable sets are designed with a connector at each end and each of the other components to be interconnected is provided with a connector to mate in some fashion to one or more cable sets. Components and cable sets are merely plugged together, virtually eliminating the need for "hard" wiring.
The first commercial cable sets for flexible wiring systems were made from rubber sheathed cable. Because Underwriter's Laboratory ("UL") would only accept cable sets with flexible metal armor sheathing for listing as approved products, rubber sheathed cable gave way to cable sheathed in flexible metal armor. By means of factory fabricated pre-assembled cables of varying length, with connectors attached on each end, and arrangements of distribution modules, switching modules and loads (such as lighting fixtures) provided with suitable connectors, a complete branch circuit wiring system can be installed, with the need for conventional conduit and wire being virtually eliminated. Thus, much less labor is required to install a flexible wiring system than is required for the installation of a conventional "hard" wiring system. Flexible wiring systems have further advantages such as providing flexibility for future changes in layout. Lighting fixtures, receptacles and switches can be easily relocated simply by unplugging, rearranging and plugging in at new locations.
However, prior flexible wiring systems and the components therefor have substantial disadvantages attendant to their manufacture and use. Some of these drawbacks include high parts counts and expensive-to-manufacture component designs, contact designs unsuitable for making and breaking connections under load, connector designs deficient in terms of mechanical stability and secure connector locking, and difficult- or expensive-to-install receptacle designs for adapting light fixtures and the like to flexible wiring systems.